Helping people with computers... one answer at a time.
Originally CD burners and PCs were slow, and it was a bad idea to try to do anything else while a CD was being burned. I'll look at the situation today.
It used to be that it was risky to switch to another Windows app while your CD burner was working. It could cause corruption on the CD. Is this still the case with modern CD burners? I've still kept up the habit of leaving the machine alone while burning, but would love to be doing something else in the background if it's now safe.
You and I have had the same experience.
"Back in the day" once you started a CD burning you were wise to keep your hands off the computer until it was done. "Back in the day" that often meant for a full hour if the disc was to be filled, as the CD writers worked at 1x speed.
More than a few things have changed since then.
As a result, "multi-task within reason" is my response.
But I guess I need to explain what I mean by reason.
While burning CDs and DVDs, which I do regularly, I multi-task away within reason. That means that I'm regularly reading email, browsing the web and such while burns are happening.
I think several things have changed over the years that now combine to make it much safer to continue using your computer while you're burning something:
CPUs are faster, so any computational limitations of the burning process aren't as big a deal in comparison. This also means that most other things you might do won't have as large an impact on the needs of the burning process.
The software that does the burning (I use ImgBurn) is, I think, better at buffering and prioritizing its work. You'll often see software "filling buffers" before the media even starts spinning.
The drives themselves have larger internal buffers and are more resilient to interruption. In addition to the buffering of the previous point, I regularly see an additional "hardware buffer" being filled as well. The net result is that the drive can, on its own and without additional data from the PC, keep burning for several seconds. That's not something that the old drives were capable of.
Multi-speed drives are able to slow down and burn more slowly if the media is difficult to burn, or presumably if the CPU isn't sending data to be written to the drive fast enough.
The limiting factor, after the write-speed of the burner itself, is the data transfer speed from the hard disk to the burner. Disks are faster and the I/O channels over which data is transferred are faster than they were in days past.
Windows itself has changed. In particular the "cooperative multi-tasking" that essentially mimicked true multi tasking in Windows 9x versions was replaced with a true multi-tasking operating system in the switch to NT, Windows 2000, XP and later. The older operating systems could easily be hung up by almost any application taking a little too long to do its work.
Now, all that being said, I do shy away from disk intensive activity and strongly recommend that you do the same. I also avoid doing things that would really hog the CPU, but that's about it.
The good news also is that most CD-burning software will detect and alert to errors rather than just leave you with a corrupt disk. If you suspect a problem is possible, most also have a separate "verify" step. ImgBurn will, in fact, eject and retract the newly burned CD (if it's in a tray) prior to reading and verifying the CD contents.
Bottom line: I'm sure a problem can still happen but it's much harder to get to than we remember.
(Full disclosure: the person asking was a friend and former co-worker at Microsoft. For all I know we were using the same CD-burning equipment ... "back in the day".)